The present invention relates to boat lift structures for raising and supporting boats, and more particularly to boat lift structures which are carried onboard during use of the boat. Examples of such prior art onboard boat lift structures are provided in U.S. Pat. No. 5,042,417 to Raymond, U.S. Pat. No. 5,558,034 to Hodapp, and in a series of patents (U.S. Pat. Nos. 6,907,835, 6,983,707, 7,051,665, 7,156,030, 7,267,066 and 7,318,385) to Derner et al. All these mentioned patents are incorporated by reference.
In general terms, these existing onboard lift structures involve a plurality of legs which are pivotable relative to the boat, from a stowed position wherein the legs are generally parallel to the deck of the boat or horizontal water surface, to a downwardly extended support position wherein the legs are relatively upright, i.e., significantly more upright than in the stowed position. A pad is provided on the free end of the legs which once contacting the ground is intended to provide a stationary foot location. The legs can be independently operable, as disclosed in the Derner et al. patents, or be operable jointly in pairs, as disclosed in the Raymond and Hodapp patents.
While these prior art onboard boat lift structures provide benefits, they also have some shortcomings. With the Raymond structure, the stowed position of the legs and the pads is on the outside of the sides of the boat. This permits easy viewing of the legs and pads during deployment. This location also provides a wide base, with the pads separated by a distance wider than the width of the boat. At the same time, however, the stowed position detracts aesthetically from the appearance of the boat during use, and increases wind resistance during use of the boat. The stowed position of the legs and pads can also interfere with people climbing in and out of the side of the boat.
In contrast to the Raymond structure, the Hodapp and Derner structures are mounted underneath the deck of the boat and interior to the position of pontoons on the bottom of the boat. This location is concealed during the stowed position, does not significantly affect wind resistance during use of the boat, and does not interfere with ingress and egress from the boat. However, the narrow base creates a potentially unstable stand for the pontoon boat when raised, and a stiff wind, particularly if coupled with angled placement or loading of the boat, could create a potentially dangerous or damaging possibility of tipping or flipping the boat off of the narrow base. The legs and pads cannot be viewed during deployment, making deployment more difficult. The drive systems for the legs, and particularly the independent, screw drives of the Derner system, increase the cost of the system. Better structures and methods of lifting boats are needed.